AROUND MID-October last year an Angel made its first flight. It was the culmination of months and months of hard, dedicated work by Johan Lok’s Wonderboom, Pretoria-based maintenance and repair company, Warbirds, and structural analysis and modification planning support from Francois Jordaan’s Aerostruct Consulting.
On its maiden flight, this Angel was under the control of Carlos Cabralm, a South African Civil Aviation Authority Class II test pilot who helped with the consulting and flight test support. ‘Plane spotters who might have been around for the Angel’s first flight could have correctly assumed that this Angel was, in fact, a turboprop-powered and modified Atlas Aircraft CAM Kudu (see World Airnews, November 2009).
Some may even have assumed that this was the first Kudu ever to have been powered by a turboprop engine. They would have been wrong for much-modified Kudus in a Cessna Caravan look-alike configuration, have been flying in Canada and the USA since 2007 and one even won the top award at the 2008 Sun ‘n Fun in Florida, USA, and, a few months later, the top award at the EAA’s AirVenture 2008 show in Oshkosh.
The Canadian-built Grizzly version of the original Kudu.
That aircraft conversion has been dubbed the Grizzly. It was fitted with floats. The more sharp-eyed spotters would have realised that it had a wingspan about a two metres longer than that of the Kudu, and two extra windows which gave it the Caravan look; had two large cargo doors at the rear and was powered by a Pratt & Whitney Canada PT- 6 engine as against the Angel’s Czech-built Walter M601D powerplant.
This all came to light when World Airnews received an email from an Air Canada airline pilot, Vincent Gagnon- Pouliot, a former bush pilot with some 12 000 hours to his credit. He is also president of Aerotek Aviation Inc., which he described as a Pratt & Whitney turbine conversion firewall forward company based in Quebec. He wrote: “Following the reading of your article on the Turbine Kudu in South Africa, I was amazed to realise that we have been doing the same thing for some time here with Kudus. In 2007, we bought four AI60 (Airmacchi) airframes in the USA to convert each with a PT6 turbine engine to compete with the de Havilland Turbo Beaver, but in a more affordable way for the private owner in the experimental, non-certified category, like your turbine Atlas Angel/Kudu.
The Angel, the South African turboprop conversion of the Kudu.
“When I flew the A160 (Kudu) for the first time in its normal configuration, I realised there were big control problems (as Des Barker mentioned in his article on the Kudu) and just about enough lift for its gross weight with the actual wingspan (4 500 pounds). I also found the name of an old engineer who worked on the original design of the A160 and learned from him that the weakest part of this aircraft is the tail fin.’ Gagnon-Pouliot continued: “After looking through all that, we decided that we needed more lift, lateral control, better aileron control (easier to turn since the original ailerons were very hard to turn and the yoke doesn’t have enough travel left and right) and stronger tail fin if we wanted a safe, strong as close as possible to a certified aircraft. “When we de-skinned the wings, we also realised that the original wing did not have a standard strong spa, but it is a stringer wing, not solid enough the way it is to install an extension (like they do on a Cessna 185 or C206 wing extension).
“Although we wanted to keep the same wing airfoil to keep the flying characteristics intact, we wanted a longer wing for more lift, and a stronger wing, too (attachments to the fuselage and fuselage wing attachment spar re-enforced, too). This was very important so that the power increase of the turbine could be accommodated,” Gagnon-Pouliot wrote. “The airframe was built for a maximum of 400 hp, the wing attachments are made for that; the tail attachments are made for that as well. So if you switch an engine from 400 hp (or 340) with about only 400 pounds of torque on take-off, to a 600 or 700 shp turbine engine with 1 300 to 1 500 pounds of torque on takeoff, you cannot expect the original wing and tail attachments to be strong enough.
“Since we have access to the Turbo- Beaver technical data, we used a lot of the certified Turbine DHC-2 re-enforcement design for the new Turbine Grizzly. We made a new wing jig, three-feet longer at the root for each wing (using the old wing for dimensions) and created a new wing structure design with new ribs – a big strong spar with wet fuel tanks containing 90 gallons on each side. With this fuel quantity you can get five hours with the PT6 at 8 000 feet and an indicated airspeed of 135 knots (or 140 knots true at 3 000 feet and 145 at 10 000 feet on wheels.
“The wing span is now 45,5 feet (13,87 metres) instead of 39 feet with wing struts twice as big as before and attachments four times stronger. We also get a lot more lift and a new 5 500-pound (2 495 kg) gross weight for a lower wing loading than the original wing,” Gagnon-Pouliot said. The Aerotek Aviation team also added a dorsal fin to re-enforce the tail attachment and lateral control for the fin and a bigger rudder. The bell cranks were modified to give better travel and movement on the ailerons, and obviously a new cowling for the PT6.
Other modifications included the reskinning of 90% of the fuselage. New spring steel-type landing gear (Caravan style) to support the higher gross weight, and the yoke control was modified to permit a central radio stack installation.
The conversion from Kudu to Grizzly took a year and included an upgraded cockpit with a fully 3D synthetic vision EFIS panel and digital engine gauges. The Grizzly has accommodation for a pilot and five passengers in its deluxe configuration and the cabin design is such the centre seats can be turned around to form club class seating. Alternatively, if used for parachute jumping, up to eight skydivers and the pilot can be carried easily.
The empty weight on wheels with the deluxe interior is 2 875 pounds (1 304 kg) and gross weight is 5 400 lbs (2 450 kg) with the new wings. Useful load is 2 525 pounds (1 145 kg). Even with full fuel, the Grizzly can still carry 1 425 pounds (646 kg). At half load it will climb at 2 000 ft/min plus and at gross weight will climb at 1 100 ft/min – both rates at 90 knots climb speed. On wheels at gross weight, it requires only 150 metres to takeoff.
The Grizzly in flight.
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